Surface inspection apparatus

ABSTRACT

A surface inspection apparatus includes units illuminating repetitive patterns formed on a surface of a suspected substance and measuring a variation in an intensity of regular reflection light caused by a change in shapes of the repetitive patterns, units illuminating the repetitive patterns with linearly polarized light, setting an angle formed between a repetitive direction of the repetitive patterns and a direction of a plane of vibration of the linearly polarized light at a tilt angle, and measuring a variation in a polarized state of the regular reflection light caused by the change in the shapes of the repetitive patterns, and a unit detecting a defect of the repetitive patterns based on the variation in the intensity and the variation in the polarized state of the regular reflection light.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of InternationalApplication No. PCT/JP2007/000496, filed May 9, 2007, designating theU.S., in which the International Application claims a priority date ofMay 10, 2006, based on prior filed Japanese Patent Application No.2006-131120, the entire contents of which are incorporated herein byreference.

BACKGROUND

1. Field

The present application relates to a surface inspection apparatusexecuting a defect inspection of repetitive patterns formed on a surfaceof a suspected substance.

2. Description of the Related Art

There is known an apparatus which irradiates illumination light forinspection to repetitive patterns formed on a surface of a suspectedsubstance (semiconductor wafer, liquid crystal substrate and the like,for instance), and executes a defect inspection of the repetitivepatterns based on light generated from the repetitive patterns at thistime. There are various methods applied to this inspection apparatus inaccordance with a type of light (for instance, diffraction ray,scattered light, regular reflection light, and the like) generated fromthe repetitive patterns. Further, regarding the illumination light forinspection to be used, an apparatus using unpolarized light, anapparatus using linearly polarized light (refer to Patent Document 1:International Publication Pamphlet WO 2005/040776, for instance), andthe like are known. Each of these inspection apparatus can collectivelydetect defects of the repetitive patterns in a relatively wide area(whole area, for instance) on the surface of the suspected substance,and can execute a defect inspection in a high throughput manner.

However, there are various types of defects of repetitive patterns. Forexample, as a typical type of defect generated at a time of an exposureon a suspected substance, a defocus defect and a dose defect can becited. Under the present situation, it is difficult to separately detectthe various types of defects in the aforementioned apparatus, so that aplurality of types of defects are collectively detected. However, as aresult of repeated studies by the present inventors, it has been foundthat a detection sensitivity to the defect largely depends on acombination of the type and a detection method of the defect, and with acertain specific detection method, sufficient detection sensitivitycannot be obtained depending on the type of the defect. Further, it alsohas been found that even a defect in which sufficient detectionsensitivity thereto cannot be obtained with a certain detection methodcan be detected in a highly sensitive manner by using another detectionmethod.

SUMMARY

A proposition is to provide a surface inspection apparatus capable ofsecuring sufficient detection sensitivity to a plurality of types ofdefects of repetitive patterns.

A surface inspection apparatus includes a first measuring unit, a secondmeasuring unit, and a detecting unit. The first measuring unitilluminates repetitive patterns formed on a surface of a suspectedsubstance and measures, based on a intensity of regular reflection lightgenerated from the repetitive patterns, a variation in the intensitycaused by a change in shapes of the repetitive patterns. The secondmeasuring unit illuminates the repetitive patterns with linearlypolarized light, sets an angle formed between a repetitive direction ofthe repetitive patterns and a direction of a plane of vibration of thelinearly polarized light at the surface at a tilt angle, and measures,based on a polarized state of the regular reflection light generatedfrom the repetitive patterns, a variation in the polarized state causedby the change in the shapes of the repetitive patterns. The detectingunit detects a defect of the repetitive patterns based on the variationin the intensity measured by the first measuring unit and the variationin the polarized state measured by the second measuring unit.

Another surface inspection apparatus includes an illuminating unit, alight receiving unit, a first processing unit, a second processing unit,and a detecting unit. The illuminating unit irradiates illuminationlight to repetitive patterns formed on a surface of a suspectedsubstance and having a first polarization plate capable of beinginserted into or removed from a light path of the illumination light.The light receiving unit outputs a light receiving signal based onregular reflection light generated from the repetitive patterns, and hasa second polarization plate capable of being inserted into or removedfrom a light path of the regular reflection light and whose transmissionaxis intersects a transmission axis of the first polarization plate. Thefirst processing unit disposes either of the first polarization plate orthe second polarization plate in the light path, inputs the lightreceiving signal relating to a intensity of the regular reflection lightfrom the light receiving unit, and measures a variation in the intensitycaused by a change in shapes of the repetitive patterns. The secondprocessing unit disposes both the first polarization plate and thesecond polarization plate in the light paths, sets an angle formedbetween a direction of a plane of vibration of linearly polarized lightirradiated to the repetitive patterns as the illumination light at thesurface and a repetitive direction of the repetitive patterns at a tiltangle, inputs the light receiving signal relating to a polarized stateof the regular reflection light from the light receiving unit, andmeasures a variation in the polarized state caused by the change in theshapes of the repetitive patterns. The detecting unit detects a defectof the repetitive patterns based on the variation in the intensitymeasured by the first processing unit and the variation in the polarizedstate measured by the second processing unit.

Further, the first processing unit may dispose a polarization plate inthe light path, the polarization plate being either of the firstpolarization plate or the second polarization plate whose transmissionaxis is orthogonal to a plane of incidence of the illumination light.

Further, the detecting unit may detect a first type of defect of therepetitive patterns based on the variation in the intensity, may detecta second type of defect of the repetitive patterns based on thevariation in the polarized state, and may designate a spot on thesurface where at least either of the first type of defect or the secondtype of defect is detected, as a final defect of the repetitivepatterns.

Further, the detecting unit may output information on the final defectby adding information on a type of the defect thereto.

Further, the first type of defect may be a dose defect generated whenperforming an exposure on the suspected substance, and the second typeof defect may be a defocus defect generated when performing an exposureon the suspected substance.

According to a surface inspection apparatus, it is possible to securesufficient detection sensitivity to a plurality of types of defects ofrepetitive patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating an entire structure of a surfaceinspection apparatus 10.

FIG. 2 is a schematic diagram of a surface of a suspected substance 20.

FIG. 3 is a view to explain an inclination state between a plane ofincidence (3A) of illumination light L1 and a repetitive direction (Xdirection) of repetitive patterns 22.

FIGS. 4( a), 4(b), and 4(c) are views to explain a defocus defect at atime of an exposure.

FIGS. 5( a), 5(b), and 5(c) are views to explain a dose defect at a timeof an exposure.

FIGS. 6( a), 6(b), and 6(c) are views to explain polarized states of theillumination light L1 and regular reflection light L2.

FIG. 7 is a view to explain an inclination state between a direction ofa plane of vibration (V direction) of the illumination light L1 and therepetitive direction (X direction) of the repetitive patterns 22.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be specifically described with referenceto the drawings.

As illustrated in FIG. 1, a surface inspection apparatus 10 of thisembodiment includes a stage 11 that supports a suspected substance 20,an alignment system 12, an illuminating system 13, a light receivingsystem 14, an image processor 15, and a controller 16.

The suspected substance 20 is, for example, a semiconductor wafer, aliquid crystal glass substrate, or the like. As illustrated in FIG. 2, aplurality of chip areas 21 are arrayed on a surface (resist layer) ofthe suspected substance 20, and a repetitive pattern 22 to be inspectedis formed in each of the chip areas 21. The repetitive pattern 22 is apattern of line-and-space such as a wiring pattern. A direction alongwhich line portions of the repetitive patterns 22 are arrayed (Xdirection) is referred to as a “repetitive direction of the repetitivepatterns 22”.

The surface inspection apparatus 10 of this embodiment is an apparatuswhich automatically executes a defect inspection of the repetitivepatterns 22 formed on a surface of the suspected substance 20 during aprocess of manufacturing a semiconductor circuit element or a liquidcrystal display element. In the surface inspection apparatus 10, thesuspected substance 20 whose surface (resist layer) is exposed anddeveloped is transferred from a cassette or a developing device by anot-illustrated transfer system and sucked to the stage 11.

The stage 11 holds fast the suspected substance 20 placed on an uppersurface thereof by, for instance, vacuum suction. Besides, the stage 11is provided with a rotary mechanism 1A. A rotary shaft of the stage 11is orthogonal to the upper surface on which the suspected substance 20is placed. The rotary mechanism 1A rotates the stage 11 in accordancewith an instruction from the controller 16, to thereby rotate thesuspected substance 20 placed on the upper surface of the stage 11.Accordingly, it is possible to rotate the repetitive direction (Xdirection in FIG. 2) of the repetitive patterns 22 of the suspectedsubstance 20 within the surface of the suspected substance 20.

While the stage 11 rotates, the alignment system 12 illuminates an outeredge of the suspected substance 20, and detects a direction of therepetitive patterns 22 on the suspected substance 20 based on a positionof an outer contour reference (a notch, for instance) along the rotatingdirection thereof provided at the outer edge. A detection result fromthe alignment system 12 is input into the controller 16, and when therepetitive direction (X direction) of the repetitive patterns 22 is setto be a desired direction, the rotation of the stage 11 is stopped.

For example, if a plane of incidence 3A of the illumination light L1irradiated to the repetitive patterns 22 from the illuminating system 13(FIG. 3) is set as a reference, the desired direction of the repetitivepatterns is defined by an angle φ formed between a direction of theplane of incidence 3A and the repetitive direction (X direction) of therepetitive patterns 22. In this embodiment, the angle φ is set at a tiltangle (0°<φ<90°). The angle φ is, for example, 45°. Note that the planeof incidence 3A is a plane including an irradiation direction of theillumination light L1 and a normal on the surface of the suspectedsubstance 20.

The illuminating system 13 is a unit irradiating the illumination lightL1 for inspection to the repetitive patterns 22 formed on the surface ofthe suspected substance 20 (FIG. 2 and FIG. 3) and includes a lamphouse31, a light guide fiber 33, a polarization plate 34, and a concavereflecting mirror 35. The illuminating system 13 is a telecentricoptical system with respect to a side of the suspected substance 20.

Although the illustration is omitted, inside the lamphouse 31, a lightsource, a wavelength selection filter, an ND filter used in a lightquantity adjustment, and the like are embedded. The light source is aninexpensive discharge light source such as a halogen lamp, a metalhalide lamp, and a mercury lamp. The wavelength selection filterselectively transmits a bright-line spectrum of a predeterminedwavelength among light radiated from the light source.

The light guide fiber 33 transmits the light radiated from the lamphouse31 and emits a divergent light flux of illumination light (unpolarizedlight).

The polarization plate 34 is disposed in the vicinity of an emission endof the light guide fiber 33, and its transmission axis is set at apredetermined direction. Subsequently, the polarization plate 34converts the divergent light flux of illumination light (unpolarizedlight) emitted from the light guide fiber 33 to light in a polarizedstate (namely, linearly polarized light) according to the direction ofthe transmission axis. The direction of the transmission axis of thepolarization plate 34 is parallel with the plane of incidence 3A of theillumination light L1 with respect to the repetitive patterns 22 (FIG.3).

The concave reflecting mirror 35 is a reflecting mirror in which aninner side of a spherical surface is a reflection surface, and isdisposed so that its front-side focal point substantially matches theemission end of the light guide fiber 33 and its rear-side focal pointsubstantially matches the surface of the suspected substance 20.Accordingly, the divergent light flux of illumination light (linearlypolarized light) from the polarization plate 34 is collimated at theconcave reflecting mirror 35, and irradiated to the repetitive patterns22 on the suspected substance 20 as the illumination light L1 forinspection.

Further, the aforementioned polarization plate 34 is structured so thatit can be inserted into or removed from a light path between the lightguide fiber 33 and the concave reflecting mirror 35 (namely, light pathof the divergent flux of illumination light), and can retract from aposition in the light path shown by a solid line to a position shown bya dotted line in FIG. 1. In order to realize this, a rotary shaft of adrive motor 4A is coupled to the polarization plate 34. The polarizationplate 34 can rotate around the rotary shaft of the drive motor 4A as acenter. The rotation (insertion and removal) of the polarization plate34 is conducted by the drive motor 4A in accordance with the instructionfrom the controller 16.

When the polarization plate 34 is retracted from the light path, thedivergent flux of illumination light (unpolarized light) from the lightguide fiber 33 is directly incident to the concave reflecting mirror 35.Subsequently, the light is collimated at the concave reflecting mirror35 and irradiated to the repetitive patterns 22 on the suspectedsubstance 20 as the illumination light L1 for inspection.

As described above, in the aforementioned illuminating system 13, therepetitive patterns 22 can be illuminated by the linearly polarizedillumination light L1 when the polarization plate 34 is disposed in thelight path between the light guide fiber 33 and the concave reflectingmirror 35, and it can be illuminated by the unpolarized illuminationlight L1 t when the polarization plate 34 is retracted from the lightpath.

Further, in any cases, the illumination light L1 is incident torespective points of a relatively wide area (whole area, for instance)of the surface of the suspected substance 20 from a diagonal upperdirection in a substantially constant angle condition. This can berealized by diverging the light flux from the lamphouse 31 and thencollimating it at the concave reflecting mirror 35. If the whole surfaceof the suspected substance 20 is illuminated, it becomes possible tocollectively detect the defects of the repetitive patterns 22 in thewhole surface and to execute the defect inspection in a high-throughputmanner.

When the repetitive patterns 22 are illuminated by using theaforementioned linearly polarized or unpolarized illumination light L1,regular reflection light L2 is generated from the repetitive patterns22. Note that in this embodiment, there is no chance that the repetitivepattern 22 generates diffraction ray when the illumination light L1 isirradiated thereto, since a pitch of the repetitive pattern 22 issufficiently small compared to a wavelength of the illumination lightL1.

The surface inspection apparatus 10 of this embodiment illuminates therepetitive patterns 22 on the surface of the suspected substance 20 withthe linearly polarized or unpolarized illumination light L1, guides theregular reflection light L2 generated from the repetitive patterns 22 atthis time to the light receiving system 14, and executes the defectinspection of the repetitive patterns 22 based on the intensity or thepolarized state of the regular reflection light L2.

The light receiving system 14 is a unit outputting a light receivingsignal based on the regular reflection light L2 generated from therepetitive patterns 22, and includes a concave reflecting mirror 36, apolarization plate 37, a condenser lens 38, and an image sensor 39. Thelight receiving system 14 is a telecentric optical system with respectto the side of the suspected substance 20.

The concave reflecting mirror 36 having the same structure as that ofthe concave reflecting mirror 35 of the illuminating system 13 reflectsthe regular reflection light L2 generated from the repetitive patterns22 on the surface of the suspected substance 20 to convert it to acondensed light flux, and then guides it toward the polarization plate37.

Subsequently, the light (regular reflection light L2) from the concavereflecting mirror 36 transmits the polarization plate 37, and then isincident to the image sensor 39 via the condenser lens 38.

Note that the polarization plate 37 is structured so that it can beinserted into or removed from a light path between the concavereflecting mirror 36 and the condenser lens 38 (namely, light path ofthe condensed light flux of regular reflection light L2), and canretract from a position in the light path shown by a solid line to aposition shown by a dotted line in FIG. 1. In order to realize this, arotary shaft of a drive motor 7A is coupled to the polarization plate37. The polarization plate 37 can rotate around the rotary shaft of thedrive motor 7A as a center. The rotation (insertion and removal) of thepolarization plate 37 is conducted by the drive motor 7A in accordancewith the instruction from the controller 16.

When the polarization plate 37 is retracted from the light path, theregular reflection light L2 from the repetitive patterns 22 is directly(without passing through the polarization plate 37) incident to theimage sensor 39. Further, when the polarization plate 37 is disposed inthe light path, the regular reflection light L2 from the repetitivepatterns 22 is incident to the image sensor 39 via the polarizationplate 37.

When the polarization plate 37 is disposed in the light path, thedisposed position thereof is in the vicinity of the condenser lens 38,and its transmission axis is set in a predetermined direction asfollows. Specifically, the direction of the transmission axis of thepolarization plate 37 is set to be orthogonal to the plane of incidence3A of the illumination light L1 (FIG. 3).

Subsequently, regardless of the insertion/removal state of thepolarization plate 37, a reflected image of the surface of the suspectedsubstance 20 is formed at an imaging area of the image sensor 39 inaccordance with the regular reflection light L2 from the respectivepoints (repetitive patterns 22) on the surface of the suspectedsubstance 20.

The image sensor 39 is disposed at a position conjugate with theposition of the surface of the suspected substance 20. The image sensor39 is, for example, a CCD image sensor or the like, which performsphotoelectric conversion on the reflected image of the suspectedsubstance 20 formed at the imaging area and outputs image signals(information regarding the regular reflection light L2) to the imageprocessor 15.

Based on the image signals output from the image sensor 39, the imageprocessor takes the reflected image of the suspected substance 20.Subsequently, it performs a process to detect a defect of the repetitivepatterns 22.

Next, a procedure of the defect inspection of the repetitive patterns 22in the surface inspection apparatus 10 of this embodiment will beexplained. Here, an explanation will be made regarding a detection ofdefects at a time of an exposure on the suspected substance amongdefects of the repetitive patterns 22 (namely, defocus defect and dosedefect). Incidentally, the defect at the time of the exposure appears ineach shot area of the suspected substance 20.

The defocus defect is a defect generated when the amount of defocus atthe time of the exposure on the suspected substance 20 (shift amount ofa focus position when performing the exposure using an exposureapparatus) exceeds a tolerance level, and is appeared as a change in ashape of the repetitive pattern 22 (namely, change in inclined angles θof edges E₁ and E₂ of the line portion), as illustrated in FIGS. 4( a),4(b), and 4(c).

When the focus at the time of the exposure takes a proper value (FIG. 4(a)), the edges E₁ and E₂ of the repetitive pattern 22 take verticalforms. When the focus value at the time of the exposure deviates fromthe proper value (FIGS. 4( b) and 4(c)), the edges E₁ and E₂ areinclined (θ≠90°). However, a pitch P of the repetitive pattern 22 and aline width D of the line portion are never changed depending on thedefocus amount.

The dose defect is a defect generated when the amount of dose at thetime of the exposure on the suspected substance 20 (exposure amount whenperforming the exposure using the exposure apparatus) exceeds or fallsbelow a tolerance level, and is appeared as a change in a shape of therepetitive pattern 22 (namely, change in the line width D of the lineportion), as illustrated in FIGS. 5( a), 5(b), and 5(c). When the doseamount at the time of the exposure takes a proper value (FIG. 5( a)),the line width D of the repetitive pattern 22 takes a design value. Whenthe dose amount at the time of the exposure deviates from the propervalue (FIGS. 5( b) and 5(c)), the line width D takes a value differentfrom the design value.

However, the pitch P of the repetitive pattern 22 and the inclinedangles θ of the edges E₁ and E₂ of the line portion are never changeddepending on the dose amount.

As a result of repeated studies by the present inventors regarding adetection of such two types of defects (defocus defect and dose defect),it has been found that by using two detection methods as follows, it ispossible to separately detect the defocus defect and the dose defect.

With the use of a first detection method, sufficient detectionsensitivity to the defocus defect can be secured, but, it is notpossible to obtain sufficient detection sensitivity to the dose defect.Accordingly, if the first detection method is employed, the defocusdefect of the repetitive patterns 22 can be selectively detected.

On the contrary, with the use of a second detection method, sufficientdetection sensitivity to the dose defect can be secured, but, it is notpossible to obtain sufficient detection sensitivity to the defocusdefect. Accordingly, if the second detection method is employed, thedose defect of the repetitive patterns 22 can be selectively detected.

The surface inspection apparatus 10 of this embodiment can realize boththe first detection method and the second detection method bystructuring such that the polarization plate 34 of the illuminatingsystem 13 can be inserted into or removed from the light path, and thepolarization plate 37 of the light receiving system 14 can be insertedinto or removed from the light path.

When executing the defect inspection of the repetitive patterns 22, thecontroller 16 gives instructions to control the drive motor 4A of theilluminating system 13 and the drive motor 7A of the light receivingsystem 14 so that the rotations (insertion and removal) of the twopolarization plates 34 and 37 are conducted in a conjunction manner.Specifically, when either of the polarization plates 34 or 37 isdisposed in the light path, the other one is also disposed in the lightpath, and when either of the polarization plates is retracted, the otherone is also retracted from the light path. Subsequently, underrespective situations where both the polarization plates 34 and 37 aredisposed or retracted, processes as follows are conducted.

First, in order to selectively detect the defocus defect of therepetitive patterns 22 using the first detection method, both thepolarization plates 34 and 37 are disposed in the light paths. At thistime, the direction of the transmission axis of the polarization plate34 of the illuminating system 13 is parallel with the plane of incidence3A of the illumination light L1 (FIG. 3), as described above. Further,the direction of the transmission axis of the polarization plate 37 ofthe light receiving system 14 is orthogonal to the plane of incidence 3Aof the illumination light L1. Specifically, the two polarization plates34 and 37 are disposed so that their transmission axes are orthogonal toeach other (disposition in a cross-Nicole state).

Subsequently, the repetitive patterns 22 are illuminated by the linearlypolarized illumination light L1 obtained via the polarization plate 34of the illuminating system 13, and the regular reflection light L2generated from the repetitive patterns 22 at this time is incident tothe image sensor 39 via the polarization plate 37 of the light receivingsystem 14.

Here, in this embodiment, the linearly polarized illumination light L1is p-polarized light. In other words, as illustrated in FIG. 6( a), aplane (plane of vibration of the illumination light L1) including anadvancing direction of the illumination light L1 and a vibrationdirection of an electric (or magnetic) vector is included in the planeof incidence (3A) of the illumination light L1.

Therefore, when setting the angle θ formed between the direction of theplane of incidence 3A of the illumination light L1 (FIG. 3) and therepetitive direction (X direction) of the repetitive patterns 22 at atilt angle (0°<φ<90°), the angle φ formed between the direction of theplane of vibration of the illumination light L1 (V direction) at thesurface of the suspected substance 20 and the repetitive direction (Xdirection) of the repetitive patterns 22 can also be set at a tilt angle(0°<φ<90°), as illustrated in FIG. 7. The angle θ is, for example, 45°.

In other words, the linearly polarized illumination light L1 is incidentto the repetitive patterns 22 in a state where the direction of theplane of vibration (V direction in FIG. 7) at the surface of thesuspected substance 20 is inclined by the angle φ (45°, for instance)with respect to the repetitive direction (X direction) of the repetitivepatterns 22, namely, in a state where it diagonally crosses therepetitive patterns 22.

Such a state of angle formed with the illumination light L1 and therepetitive patterns 22 is constant over the entire surface of thesuspected substance 20. Note that even when an angle of 45° is insteadexpressed as an angle of 135°, 225° or 315°, the state of angle betweenthe illumination light L1 and the repetitive patterns 22 is the same.

Subsequently, when the repetitive patterns 22 are illuminated by usingthe aforementioned illumination light L1 (linearly polarized light), anovalization of the linearly polarized light (illumination light L1) isgenerated due to a form birefringence caused by an anisotropy of therepetitive patterns 22, resulting that elliptically polarized regularreflection light L2 (FIG. 6( b)) is generated from the repetitivepatterns 22.

The ovalization of the linearly polarized light generated by therepetitive patterns 22 means that there is generated a new polarizationcomponent L3 (FIG. 6( c)) being orthogonal to a plane of vibration(here, which matches the plane of incidence of the illumination lightL1) of the linearly polarized light incident to the repetitive patterns22.

Further, the extent of the ovalization of the linearly polarized lightcan be represented by a size of the new polarization component L3 (FIG.6( c)), and it largely changes depending on the change in the inclinedangles θ of the edges E₁ and E₂ of the line portion of the repetitivepattern 22 (defocus defect) illustrated in FIGS. 4( a), 4(b), and 4(c),which was found out by the studies of the present inventors. Further, itwas also found out that there is very little dependency on the change inthe line width D of the line portion (dose defect) illustrated in FIGS.5( a), 5(b), and 5(c).

Namely, it was found that in the respective points (repetitive patterns22) on the surface of the suspected substance 20, even when the shape ofthe repetitive pattern 22 changes due to the change in the defocusamount or the dose amount when performing the exposure on the suspectedsubstance 20 (FIGS. 4( a), 4(b), and 4(c) and FIGS. 5( a), 5(b), and5(c)), the extent of the ovalization of the linearly polarized light(size of the polarization component L3 in FIG. 6( c)) is changed only bythe change in the inclined angles θ of the edges E₁ and E₂ (defocusdefect) illustrated in FIGS. 4( a), 4(b), and 4(c).

Further, it was also found that, as a tendency, the extent of theovalization of the linearly polarized light (size of the polarizationcomponent L3 in FIG. 6( c)) becomes largest when the edges E₁ and E₂ ofthe line portion take vertical forms as illustrated in FIG. 4( a) (whenfocus at the time of the exposure takes a proper value), and it becomessmaller as the inclined angles θ of the edges E₁ and E₂ deviate from 90°as illustrated in FIGS. 4( b) and 4(c) (focus value at the time of theexposure deviates from the proper value).

As a result of such an ovalization of the linearly polarized light, theelliptically polarized regular reflection light L2 (FIG. 6( b)) isgenerated from the repetitive patterns 22. Note that since the specificdescription regarding the ovalization has been made in InternationalPublication Pamphlet WO 2005/040776 already applied by the presentapplicant, a detailed explanation thereof will be omitted here. Further,as described above, since the pitch of the repetitive pattern 22 issufficiently small compared to the wavelength of the illumination lightL1, there is no chance that the diffraction ray is generated from therepetitive patterns 22.

The elliptically polarized regular reflection light L2 (FIG. 6( b))generated from the repetitive patterns 22 when the linearly polarizedillumination light L1 is irradiated thereto includes the aforementionednew polarization component L3 (FIG. 6( c)) generated by the ovalizationof the linearly polarized light, and the size of the polarizationcomponent L3 represents a polarized state of the regular reflectionlight L2. Note that, as will be seen from the description above, thepolarized state of the regular reflection light L2 (size of thepolarization component L3 in FIG. 6( c)) largely changes depending onthe change in the inclined angles θ of the edges E₁ and E₂ of therepetitive pattern 22 (defocus defect) illustrated in FIGS. 4( a), 4(b),and 4(c).

Therefore, in the first detection method, the regular reflection lightL2 generated from the repetitive patterns 22 is guided to the lightreceiving system 14 (FIG. 1), and when the light transmits thepolarization plate 37 in the light path of the light receiving system14, the polarization component L3 of the regular reflection light L2(FIG. 6( c)) is extracted. Subsequently, only the polarization componentL3 is made to be incident to the image sensor 39, and based on theoutput from the image sensor 39, the reflected image of the suspectedsubstance 20 is taken into the image processor 15.

On the reflected image of the suspected substance 20, there appearsbrightness/darkness corresponding to the size of the polarizationcomponent L3 of the regular reflection light L2 (FIG. 6( c)) generatedfrom the respective points (repetitive patterns 22) on the surface ofthe suspected substance 20, namely, brightness/darkness corresponding tothe polarized state of the regular reflection light L2. Note that thebrightness/darkness of the reflected image changes in each shot area onthe surface of the suspected substance 20, and is substantially inproportion to the size of the polarization component L3.

Further, as will be seen from the description above, thebrightness/darkness of the reflected image of the suspected substance 20largely changes depending on the change in the inclined angles θ of theedges E₁ and E₂ of the repetitive pattern 22 (defocus defect)illustrated in FIGS. 4( a), 4(b), and 4(c). As a tendency, the reflectedimage becomes brighter as the edges E₁ and E₂ take ideal forms beingcloser to vertical forms (FIG. 4( a)), and it becomes darker as theedges E₁ and E₂ deviate from the vertical forms (refer to FIGS. 4( b)and 4(c)).

Therefore, after taking the reflected image of the suspected substance20, the image processor 15 compares brightness information on thereflected image with brightness information on a reflected image of adesirable sample. The desirable sample is a sample in which a focus at atime of an exposure is maintained at a proper value and repetitivepatterns 22 with ideal forms (FIG. 4( a)) are formed on its wholesurface. Further, the brightness information on the reflected image ofthe desirable sample is assumed to indicate the highest brightnessvalue.

By setting the brightness value of the reflected image of the desirablesample as a reference, the image processor 15 measures a variationamount (namely, decrease amount) of the brightness value of thereflected image of the suspected substance 20. The obtained variationamount (decrease amount) of the brightness value represents a variationin the polarized state of the regular reflection light L2 caused by thechange in the inclined angles θ of the edges E₁ and E₂ of the repetitivepattern 22 (FIGS. 4( a), 4(b), and 4(c)).

Subsequently, the image processor 15 detects the defocus defect of therepetitive patterns 22 based on the variation amount of the brightnessvalue in the reflected image of the suspected substance 20 (namely,variation in the polarized state of the regular reflection light L2).For instance, if the variation amount of the brightness value is greaterthan a predetermined threshold value (tolerance value), it may be judgedthat there is a “defect”, on the other hand, if the variation amount isless than the threshold value, the repetitive patterns may be judged tobe “normal”. Further, it is possible to compare the variation amount ofthe brightness value in the reflected image of the suspected substance20 with a predetermined threshold value, instead of using the desirablesample.

As described above, in the first detection method, the repetitivepatterns 22 are illuminated by the linearly polarized illumination lightL1, the reflected image of the suspected substance 20 is taken inaccordance with the polarized state of the regular reflection light L2(size of the polarization component L3 in FIG. 6( c)) generated from therepetitive patterns 22, and based on the brightness/darkness of thereflected image, the variation in the polarized state of the regularreflection light L2 caused by the change in the inclined angles θ of theedges E₁ and E₂ of the repetitive pattern 22 (FIGS. 4( a), 4(b), and4(c)) is measured.

Therefore, according to the first detection method, although thesufficient detection sensitivity to the dose defect (FIGS. 5( a), 5(b),and 5(c)) cannot be obtained, it is possible to secure the sufficientdetection sensitivity to the defocus defect (FIGS. 4( a), 4(b), and4(c)) of the repetitive patterns 22, so that the defocus defect can beselectively detected. Note that if the angle φ formed between thedirection of the plane of vibration (V direction) and the repetitivedirection (X direction) in FIG. 7 is set at 45°, it is possible toprovide the highest detection sensitivity to the defocus defect of therepetitive patterns 22.

Next, in order to selectively detect the dose defect of the repetitivepatterns 22 (FIGS. 5( a), 5(b), and 5(c)) using the second detectionmethod, both the polarization plates 34 and 37 are retracted from thelight paths. At this time, the repetitive patterns 22 are illuminated bythe unpolarized illumination light L1, and the unpolarized regularreflection light L2 generated from the repetitive patterns 22 isdirectly (without passing through the polarization plate 37) incident tothe image sensor 39. Subsequently, based on the output from the imagesensor 39, the reflected image of the suspected substance 20 is takeninto the image processor 15.

Note that even when the unpolarized illumination light L1 is used, theangle φ formed between the direction of its plane of incidence 3A (FIG.3) and the repetitive direction (X direction) of the repetitive patterns22 may be set at a tilt angle (0°<φ<90°), similarly as in the firstdetection method. Namely, when shifting the detection method from thefirst detection method to the second detection method, there is no needto change the direction of the repetitive patterns 22. In the seconddetection method, it is possible to make noise light (diffraction rayand the like, for instance) generated from the repetitive patterns 22not to be guided to the light receiving system 14 by setting the angle φat a tilt angle. Note that in the second detection method, the angle φmay be set at 0°.

On the reflected image of the suspected substance 20 taken into theimage processor 15, there is appeared brightness/darkness correspondingto the intensity of the regular reflection light L2 (unpolarized light)generated from the respective points (repetitive patterns 22) on thesurface of the suspected substance 20. Note that the brightness/darknessof the reflected image changes in each shot area on the surface of thesuspected substance 20, and is substantially in proportion to theintensity of the regular reflection light L2.

Further, the brightness/darkness of the reflected image of the suspectedsubstance 20 (∝intensity of the regular reflection light L2) largelychanges depending on the change in the line width D of the line portionof the repetitive pattern 22 (dose defect) illustrated in FIGS. 5( a),5(b), and 5(c), which was found out by the studies of the presentinventors. Further, it was also found out that there is very littledependency on the change in the inclined angles θ of the edges E₁ and E₂of the line portion (defocus defect) illustrated in FIGS. 4( a), 4(b),and 4(c).

Namely, it was found that in the respective points (repetitive patterns22) on the surface of the suspected substance 20, even when the shape ofthe repetitive pattern 22 changes due to the change in the defocusamount or the dose amount when performing the exposure on the suspectedsubstance 20 (FIGS. 4( a), 4(b), and 4(c) and FIGS. 5( a), 5(b), and5(c)), the brightness/darkness of the reflected image of the suspectedsubstance 20 (∝intensity of the regular reflection light L2) is changedonly by the change in the line width D of the line portion (dose defect)illustrated in FIGS. 5( a), 5(b), and 5(c).

However, this is effective when the line width D of the line portion ofthe repetitive pattern 22 (55 nm, for instance) is shorter than the usedwavelength (436 nm, for instance). In this case, the aforementionedregular reflection light L2 is generated by an interference of light atthe line portion (resist) of the repetitive pattern 22. When the linewidth D of the line portion of the repetitive pattern 22 changes due tothe change in the dose amount at the time of the exposure, the amount ofline portion per unit area (namely, the amount of portion at which theaforementioned interference of light is generated) changes and areflectivity at the line portion changes, thereby the intensity of theregular reflection light L2 may change.

Therefore, after taking the reflected image of the suspected substance20, the image processor 15 compares brightness information on thereflected image with, for example, brightness information on a reflectedimage of a desirable sample. The desirable sample is a sample in which adose amount at a time of an exposure is maintained at a proper value andrepetitive patterns 22 with ideal forms (FIG. 5( a)), for instance, areformed on its whole surface.

By setting the brightness value of the reflected image of the desirablesample as a reference, the image processor 15 measures a variationamount of the brightness value of the reflected image of the suspectedsubstance 20. The obtained variation amount of the brightness valuerepresents a variation in the intensity of the regular reflection lightL2 caused by the change in the line width D of the line portion of therepetitive pattern 22 (FIGS. 5( a), 5(b), and 5(c)).

Subsequently, the image processor 15 detects the dose defect of therepetitive patterns 22 based on the variation amount of the brightnessvalue in the reflected image of the suspected substance 20 (namely,variation in the intensity of the regular reflection light L2). Forinstance, if the variation amount of the brightness value is greaterthan a predetermined threshold value (tolerance value), it may be judgedthat there is a “defect”, on the other hand, if the variation amount isless than the threshold value, the repetitive patterns may be judged tobe “normal”. Further, it is possible to compare the variation amount ofthe brightness value in the reflected image of the suspected substance20 with a predetermined threshold value, instead of using the desirablesample.

As described above, in the second detection method, the repetitivepatterns 22 are illuminated by the unpolarized illumination light L1,the reflected image of the suspected substance 20 is taken in accordancewith the intensity of the regular reflection light L2 generated from therepetitive patterns 22, and based on the brightness/darkness of thereflected image, the variation in the intensity of the regularreflection light L2 caused by the change in the line width D of the lineportion of the repetitive pattern 22 (FIGS. 5( a), 5(b), and 5(c)) ismeasured.

Therefore, according to the second detection method, although thesufficient detection sensitivity to the defocus defect (FIGS. 4( a),4(b), and 4(c)) cannot be obtained, it is possible to secure thesufficient detection sensitivity to the dose defect (FIGS. 5( a), 5(b),and 5(c)) of the repetitive patterns 22, so that the dose defect can beselectively detected.

When the detection of defocus defect (FIGS. 4( a), 4(b), and 4(c)) bythe first detection method and the detection of dose defect (FIGS. 5(a), 5(b), and 5(c)) by the second detection method are completed in theabove-described manner, the surface inspection apparatus 10 of thisembodiment detects a final defect of the repetitive patterns 22 based onthe two detection results.

For example, a spot on the surface of the suspected substance 20 whereat least either of the defocus defect (FIGS. 4( a), 4(b), and 4(c)) orthe dose defect (FIGS. 5( a), 5(b), and 5(c)) is detected as a finaldefect of the repetitive patterns 22. Namely, a logical sum of theresult from the first detection method and the result from the seconddetection method is determined, which is then designated as a finaldetection result.

As described above, the surface inspection apparatus 10 of thisembodiment measures the variation in the intensity or the polarizedstate of the regular reflection light L2 caused by the change in theshapes of the repetitive patterns 22 (FIGS. 4( a), 4(b), and 4(c), andFIGS. 5( a), 5(b), and 5(c)), and detects the final defect of therepetitive patterns 22 based on both of the measurement results.Accordingly, it is possible to secure the sufficient detectionsensitivity to the plurality of types of defects (defocus defect anddose defect) of the repetitive patterns 22.

Further, it is also possible to determine the cause of the defectdepending on which of the two detection methods is used to detect thedefect. Accordingly, it is also possible to output information on thefinal defect of the repetitive patterns 22 by adding information on thetype of the defect thereto. There are three types of the final defects,which are, a defect detected only by the first detection method(defocus), a defect detected only by the second detection method (dose),and a defect detected by both the first detection method and the seconddetection method (defocus/dose).

Since the surface inspection apparatus 10 of this embodiment canseparately detect the plurality of types of defects of the repetitivepatterns 22, it is effective to output the information on the finaldefect together with the information on the type of the defect andfeedback it to an exposure apparatus. By performing such a feedback, anadjustment of the exposure apparatus can be conducted in real time.

Further, it is preferable that in the surface inspection apparatus 10 ofthis embodiment, the information on the final defect of the repetitivepatterns 22 (position on the surface of the suspected substance 20) canbe display-output on one image. At this time, it is preferable to changea color and a shape of a mark, for example, for each type of the defectsso that the defects can be easily distinguished.

Modified Example

Note that in the aforementioned embodiment, the two polarization plates34 and 37 are disposed in the cross-Nicole state when detecting thedefocus defect using the first detection method, but, the presentembodiment is not limited to this. It is allowable that the respectivetransmission axes of the polarization plates 34 and 37 are set so thatthey intersect with an angle other than the vertical angle.Specifically, if the respective transmission axes of the polarizationplates 34 and 37 intersect, it is possible to execute the detection ofthe defocus defect using the first detection method. However, thedetection sensitivity to the defocus defect becomes the highest when thepolarization plates 34 and 37 are disposed in the cross-Nicole state.

Further, in the aforementioned embodiment, the transmission axis of thepolarization plate 34 of the illuminating system 13 is disposed inparallel with the plane of incidence 3A of the illumination light L1(namely, the illumination light L1 is made to be the p-polarized light)when detecting the defocus defect using the first detection method, but,the present embodiment is not limited to this. It is possible to disposethe transmission axis of the polarization plate 34 of the illuminatingsystem 13 orthogonal to the plane of incidence 3A of the illuminationlight L1 to thereby make the illumination light L1 be s-polarized light.It is also allowable that the transmission axis of the polarizationplate 34 is set so that it diagonally crosses the plane of incidence 3A.

Further, in the aforementioned embodiment, the transmission axis of thepolarization plate 37 of the light receiving system 14 is disposedorthogonal to the plane of incidence 3A of the illumination light L1when detecting the defocus defect using the first detection method, but,the present embodiment is not limited to this. It is allowable todispose the transmission axis of the polarization plate 37 of the lightreceiving system 14 in parallel with the plane of incidence 3A of theillumination light L1. The transmission axis of the polarization plate37 may be set so as to diagonally cross the plane of incidence 3A.

Further, in the aforementioned embodiment, the two polarization plates34 and 37 are retracted from the light paths when detecting the dosedefect using the second detection method, but, the present embodiment isnot limited to this. Even when either of the polarization plates 34 or37 is disposed in the light path, the dose defect can be detected basedon the variation in the intensity of the regular reflection light L2from the repetitive patterns 22.

In this case, it is preferable to dispose the polarization plate beingeither of the polarization plates 34 or 37 whose transmission axis isorthogonal to the plane of incidence 3A of the illumination light L1(polarization plate 37, in an example in FIG. 1). By disposing thepolarization plate in the above-described manner, noise light from afoundation layer of the suspected substance 20 can be reduced, whichenables to further enhance the detection sensitivity to the dose defect.

Further, when detecting the dose defect using the second detectionmethod, the respective transmission axes of the polarization plates 34and 37 may be aligned in parallel while the two polarization plates 34and 37 are disposed in the light paths. When shifting the detectionmethod from the first detection method to the second detection method,it is only required to rotate at least either of the polarization plates34 or 37 around an optical axis as a center. In this case, theinsertion/removal mechanism (drive motors 4A and 7A) of the polarizationplates 34 and 37 become unnecessary.

Further, in the aforementioned embodiment, the detection method isshifted from the first detection method to the second detection method,but, it may be shifted from the second detection method to the firstdetection method.

Further, in the aforementioned embodiment, a two-dimensional sensor suchas a CCD is used as the image sensor 39, but, a one-dimensional sensorcan also be applied. In this case, the one-dimensional sensor being animage sensor and a stage on which a semiconductor wafer (or liquidcrystal substrate) being a suspected substance is placed are moved in arelative manner, and an image of a whole surface of the semiconductorwafer (or liquid crystal substrate) is taken in such a way that theone-dimensional sensor scans the whole surface of the semiconductorwafer (or liquid crystal substrate).

The many features and advantages of the embodiments are apparent fromthe detailed specification and, thus, it is intended by the appendedclaims to cover all such features and advantages of the embodiments thatfall within the true spirit and scope thereof. Further, since numerousmodifications and changes will readily occur to those skilled in theart, it is not desired to limit the inventive embodiments to the exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope thereof.

1. A surface inspection apparatus, comprising: a first measuring unitilluminating repetitive patterns formed on a surface of a suspectedsubstance and measuring, based on an intensity of regular reflectionlight generated from the repetitive patterns, a variation in saidintensity caused by a change in shapes of said repetitive patterns; asecond measuring unit illuminating said repetitive patterns withlinearly polarized light, setting an angle formed between a repetitivedirection of the repetitive patterns and a direction of a plane ofvibration of said linearly polarized light at said surface at a tiltangle, and measuring, based on a polarized state of the regularreflection light generated from said repetitive patterns, a variation insaid polarized state caused by the change in the shapes of saidrepetitive patterns; and a detecting unit detecting a defect of saidrepetitive patterns based on the variation in said intensity measured bysaid first measuring unit and the variation in said polarized statemeasured by said second measuring unit.
 2. A surface inspectionapparatus, comprising: an illuminating unit irradiating illuminationlight to repetitive patterns formed on a surface of a suspectedsubstance and having a first polarization plate capable of beinginserted into or removed from a light path of the illumination light; alight receiving unit outputting a light receiving signal based onregular reflection light generated from said repetitive patterns, andhaving a second polarization plate capable of being inserted into orremoved from a light path of the regular reflection light and whosetransmission axis intersects a transmission axis of said firstpolarization plate; a first processing unit disposing either one of saidfirst polarization plate and said second polarization plate in the lightpath, inputting said light receiving signal relating to an intensity ofsaid regular reflection light from said light receiving unit, andmeasuring a variation in said intensity caused by a change in shapes ofsaid repetitive patterns; a second processing unit disposing both saidfirst polarization plate and said second polarization plate in the lightpaths, setting an angle formed between a direction of a plane ofvibration of linearly polarized light irradiated to said repetitivepatterns as said illumination light at said surface and a repetitivedirection of said repetitive patterns at a tilt angle, inputting saidlight receiving signal relating to a polarized state of said regularreflection light from said light receiving unit, and measuring avariation in said polarized state caused by the change in the shapes ofsaid repetitive patterns; and a detecting unit detecting a defect ofsaid repetitive patterns based on the variation in said intensitymeasured by said first processing unit and the variation in saidpolarized state measured by said second processing unit.
 3. The surfaceinspection apparatus according to claim 2, wherein said first processingunit disposes a polarization plate in the light path, the polarizationplate being either one of said first polarization plate and said secondpolarization plate whose transmission axis is orthogonal to a plane ofincidence of said illumination light.
 4. The surface inspectionapparatus according claim 1, wherein said detecting unit detects a firsttype of defect of said repetitive patterns based on the variation insaid intensity, detects a second type of defect of said repetitivepatterns based on the variation in said polarized state, and designatesa spot on said surface where at least either of said first type ofdefect and said second type of defect is detected, as a final defect ofsaid repetitive patterns.
 5. The surface inspection apparatus accordingto claim 4, wherein said detecting unit outputs information on saidfinal defect by adding information on a type of the defect thereto. 6.The surface inspection apparatus according to claim 4, wherein: saidfirst type of defect is a dose defect generated when performing anexposure on said suspected substance; and said second type of defect isa defocus defect generated when performing the exposure on saidsuspected substance.
 7. The surface inspection apparatus according claim2, wherein said detecting unit detects a first type of defect of saidrepetitive patterns based on the variation in said intensity, detects asecond type of defect of said repetitive patterns based on the variationin said polarized state, and designates a spot on said surface where atleast either of said first type of defect and said second type of defectis detected, as a final defect of said repetitive patterns.
 8. Thesurface inspection apparatus according to claim 7, wherein saiddetecting unit outputs information on said final defect by addinginformation on a type of the defect thereto.
 9. The surface inspectionapparatus according to claim 7, wherein: said first type of defect is adose defect generated when performing an exposure on said suspectedsubstance; and said second type of defect is a defocus defect generatedwhen performing the exposure on said suspected substance.